1. Field of the Invention
The present invention relates to an improved apparatus and method for the mixing, dilution, delivery and storage of chemicals within a closed system for wafer cleaning and wafer planarization within the semiconductor manufacturing industry.
2. Description of the Prior Art
Within the semiconductor manufacturing industry today, processes used in the manufacture and production of integrated circuits are extremely sensitive to contamination in the form of particulate, organic and/or metallic impurities. As such, chemical delivery systems which have been developed and utilized for the manufacture and production of wafers must be free of such impurities, down to a level of approximately twenty-five or fewer particles per milliliter, such particles being less than a fraction of a micron in size.
The chemical delivery systems which have been developed to date have proven unsatisfactory in a number of ways. Generally, there are four different types of chemical delivery systems currently in use.
The first type of system is a pump delivery system which utilizes a displacement pump, usually an air powered diaphragm type, whereby chemicals are lifted from a bulk source, driven through the pump and pushed out to the point of end-use.
Unfortunately, however, the pump delivery system has many negative attributes. The system is not suitable for continuous fab-wide operation due to the frequent need for pump maintenance. Moreover, pump failure is inevitable over time with replacement of parts or in whole necessary. Furthermore, the continuous contracting and expanding motion of the pump diaphragm causes degradation of the diaphragm material. The degraded pump material then enters into the chemical process stream, thereby causing contamination in the chemicals. Another drawback is that the pump action also causes massive impulses in the system by causing pulsed chemical flow with the result being unwanted particles forced through the particle filters, thereby increasing the chance of contamination. Finally, the pumps typically used in such systems provide only minimal amounts of lift from the bulk chemical source, which decreases the overall efficiency in the entire system.
Another system in current use is the combination pump/pressure system. Again, a pump mechanism is utilized to provide lift from the bulk chemical source into the system. Under this model, however, the chemicals are then delivered to a pressure vessel, from which gas pressure is utilized to motivate the chemical to the end-use area.
Although the negative aspects of the pump system are diminished somewhat and pump usage is reduced, the pump/pressure system still retains some negative attributes. Heavy pump maintenance is still required and pump failure is still inevitable. Continuous use will still cause pump material to degrade and enter the chemical stream, thereby causing contamination.
Yet another system in use is the vacuum/pressure system. This system utilizes both a vacuum and a pressure mechanism to motivate chemicals through a chemical storage vessel. When a vacuum is created in the vessel by the use of a vacuum pump, the decrease in pressure lifts the chemicals from the bulk source into the system. Alternatively, when pressure is induced in the vessel, chemicals are delivered to the end-use area or to any number of other intermediate vessels. By utilizing more than just a single vessel in the system, demand by the end-user and supply from the chemical bulk source can take place simultaneously. The vacuum pump, which is utilized outside the chemical flow loop, avoids the problems of degradation mentioned above.
The vacuum/pressure system also has its share of drawbacks. While the pump maintenance and degradation problems have been eliminated, other problems arise. The high vacuum and pressure cycle frequency can confuse the system sensors and cause the system to operate out-of-sequence, thereby causing backups on one end and inadequate supply of the chemicals on the other end, eventually causing a system shutdown. Moreover, the vacuum mechanism causes foaming and slurry entrainment problems in the vacuum lines. The vacuum/pressure mechanism puts unnecessary stress on the valves which control the release and buildup of pressure to motivate the chemicals, which in addition to the high cycle frequency, causes the valves to fail. Finally, a mixing stirrer must be utilized to prevent particle agglomeration on the bottom of the storage vessel. The mixing stirrer coating wears out and the mixing stirrer is less efficient at handling agglomeration problems on larger scale vessels and tanks.
The final system generally in use today is the pressure only system. By design, this system utilizes three pressure tanks for continuous fab-wide operation, one large tank for supply and storage of the chemicals and two smaller tanks for alternately receiving and transferring chemicals returning from the end-use area back to the tank. Chemicals are drawn into the system from the bulk source and are motivated by pressure injected into the system. The chemicals proceed into the storage tank, where they await use. When needed, the chemicals are pressure induced to the end-use area, after which they are returned into the smaller vessels. When level sensors utilized on the storage tank indicate that more chemicals are required, the chemicals are transferred into the storage tank from the receiving vessels. The system is simple, with less moving parts, corresponding to less down time. Unfortunately, the current pressure system is not suitable for chemical mechanical planarization ("CMP") delivery due to slurry particle agglomeration which occurs at the bottom of the pressure tank vessels.
The current chemical delivery systems also allow the mixing and dilution of chemicals from more than one batch source before delivery to the end-user. This is accomplished by utilizing pumps, vacuum or pressure to fill two or more metered vessels, whereupon the chemicals are then transferred to a mixing vessel and eventually to the end-user. Unfortunately, however, the current mixing systems may contaminate the chemicals through the mixing mechanism itself.
After the chemicals have been mixed and diluted, the chemicals may also be transferred to an intermediate holding vessel, to be stored for later use. An existing drawback, however, is that the storage tanks cannot currently be utilized in CMP slurry chemical delivery systems due to slurry agglomeration problems which occur in such storage tanks.
As such, it is a primary object of the present invention to provide a chemical delivery system to the semiconductor manufacturing industry which transfers process chemicals in a high state of purity from any bulk source and delivers them in an accurate and contaminant-free manner.
It is an additional object of the present invention to provide for a chemical delivery system for CMP process chemicals incorporating multiple storage vessels, which eliminate the slurry agglomeration in current systems, so that such chemicals may be stored without risk of CMP slurry agglomeration.
It is another additional object of the present invention to provide such a chemical delivery system that has low maintenance requirements by the significant elimination of many moving parts in existing chemical delivery systems, while increasing the accuracy of chemical dilution and delivery.